A review of prior and current flexible impeller pump technologies reveal that there are no acceptable prior art Dry Running Flexible Impeller Pumps that permit a flexible impeller pump to be run dry, even for a very few seconds, without certain catastrophic failure of the pump in general and specifically the impeller. Ironically, the very applications for which flexible impeller pumps are especially suited, are generally those types of situations where a finite source of fluids are sought to be disposed of completely where the pumping process is intended to completely pump all fluid present. It is these precise situations where a user, perhaps distracted by something else, leaves the impeller pump on to do its job emptying a vessel or fluid repository and then forgets that it has been left running, then the fluid runs dry, the pump housing runs dry and the friction of the impeller against the cam of the pump housing causes an almost immediate failure of the impeller. Any one of a number of consequences may occur as a result of being run dry. The impeller blades or vanes can rip through the bead. The bead of the impeller blades or vanes may wear flat. The bead may become pitted. The blade or vane can also experience cavitation or even tear. Lastly the blade or vane bows and sets such that the bead no longer contacts the cam. Each of these in essence lead to the same result, the pump no longer functions for its intended purpose.
Flexible impeller pumps are relatively simple devices that are easy to construct and able to pump a wide range of fluids. Impeller pumps are generally self-priming and can lift fluids several feet. Other than the motor that drives the pump the pump itself has only one moving part, namely a flexible impeller.
Most flexible impellers are molded from either neoprene or nitrile rubber with blades or vanes arranged around a hub. The end of each blade or vane has a bead, a somewhat rounded or fattened end opposite the hub. The impellers with few blades and small-diameter hubs are used to provide low-pressure, high-volume pumping capacity. Impellers with more blades or vanes and bigger hubs are used to provide lower-volume and higher-pressure pumping.
The flexible impellers are mounted inside a hollow housing that is mostly circular. A portion of this housing is indented forming a cam. The shaft of a drive motor is keyed into the hub of the flexible impeller such that when the pump's drive motor is turned on the flexible impeller will turn inside the pump's housing. As the impeller turns in the housing each blade is flexed in the cam area of the pump housing and as the impeller turns and eventually leaves the cam each blade straightens and increases the volume of the cavity formed between it and the next blade or vane. It is this expansion that causes suction which in turn then draws in the fluid being pumped. The straightened flexible impeller continues to rotate and as it does, it carries the fluid along with it. As this same blade or vane now contacts the cam it again begins to fold and compress the volume between it and the next blade. It is this compression of the fluid that creates a pressure that forces the fluid out the discharge port. This cycle continues with each next blade providing a smooth non-pulsating flow of pumped fluid.
Flexible impeller pumps are convenient and inexpensive being designed such that the fluids being pumped act as lubrication for the pump during the process of pumping. Therein, lies the problem with the current and the prior art flexible impeller pumps. Since the pump requires the fluid being pumped to be present in order to remain lubricated, once the pump runs dry the friction of the impeller against the cam portion of the pump housing will cause permanent damage to the impeller within no more than 15 to 20 seconds of dry running operation and in some cases even less.
The pump housings for impeller pumps may be made from a variety of materials. Many of the lowest cost pumps have a molded-plastic housing with a stamped steel cup or liner. The macerator pumps are designed without a steel liner. The most common housings for impeller pumps, however, are machined from cast metals, usually bronze, which have circular machined cavities. The cam, which is usually arc shaped, is screwed inside the cavity as a separate piece, and a cover plate with fluid tight gasket is then screwed onto the housing.
Examples of impeller pumps are taught in several patents such as those taught by E. C. Rumsey in U.S. Pat. No. 2,455,194, Takahashi in U.S. Pat. No. 3,832,105, and McCormick in U.S. Pat. No. 4,940,402. The Rumsey and McCormick patents each describe the impellers as having weights secured to the end of each vane or blade. The weight is added to keep the end of the vane or blade in contact with the housing wall and cam area as pressure against the vanes or blades increases. In practice, however, these prior art patents teach a pump technology wherein the rotation speed of the impeller increases, fluid will begin to pass between the impeller and the housing wall limiting the effective speed and maximum operating pressure of the pump. Rumsey also teaches a slot formed in a central bore of the impeller and a mating rib formed on the shaft of the drive motor for the pump. The impeller then is placed on the shaft such that the rib on the motor's shaft fits into the slot formed in the impeller. This key configuration is intended to reduce impeller slippage on the shaft as the shaft rotates at higher speeds and pressure within the housing increase, however, the slot may begin to slip over the rib and ultimately the impeller rotates on the shaft.
Takahashi describes a pump device that includes a flexible impeller similar to the instant application wherein the impeller is sandwiched between two plates. The flexible impeller is attached to the shaft of the pump, such that the rotation axis of the flexible impeller is aligned with the rotation axis of the shaft of the pump drive motor. The plates are either rotating on a bearing surface or suspended within the housing so that a portion of the plates bore contacts the drive motor's shaft. The inner surface of the bore on which each plate rotates is especially subject to wear especially if the pump is run dry.
Maki describes in U.S. Pat. No. 6,203,302 a high pressure fluid forcing pump that has a cavity adaptable for receiving a flexible impeller assembly rotatable within the cavity of the pump housing. The flexible impeller assembly includes a flexible impeller engaged between two bearing plates and having tips fixed to the bearing plates adjacent an outer circumference of the bearing plates. Maki further teaches a flexible impeller assembly that includes a locking arrangement that ensures that the impeller rotates about the motor shaft of the pump. The motor's shaft is positioned in the cavity of the pump's housing, and the rotational axis of the shaft and impeller are offset from the longitudinal axis of the cavity and the two bearing plates. Despite its improvement over E. C. Rumsey in U.S. Pat. No. 2,455,194, Takahashi in U.S. Pat. No. 3,832,105, and McCormick in U.S. Pat. No. 4,940,402, Maki also fails to teach a flexible impeller pump that may be run dry for any more than just a few seconds without permanently damaging the impeller and/or the pump.
While each of these prior art flexible impeller pump devices fulfill their respective particular objectives and requirements, and are most likely quite functional for their intended purposes, it will be noticed that none of the prior art cited disclose an apparatus and/or method of manufacture that is capable of being run dry for extended periods of time without pump failure.
As such, there apparently still exists the need for a new and improved flexible impeller pump to maximize the benefits to the user and minimize the risks of expensive damage to the pump when it is run dry.
In this respect, the present invention disclosed herein substantially corrects these problems and fulfills the need for such a device.